OS5B-2:GAS HYDRATE DEPOSIT IN THE SEA OF MARMARA: FURTHER EVIDENCES OF ITS CONNECTION WITH A PETROLEUM SYSTEM

Marie MUSY1,2, Hailong LU3*, Livio RUFFINE1*, Thomas LORENSON4, L. Igor MOUDRAKOVSKI3, Vivien GUYADER1, Jöel ETOUBLEAU1, Sandrine ChÉron1, Céline GRALL1,5, Nicolas GAYET6, Alexis De PRUNELé1, Jean-Pierre DONVAL1, Chris RATCLIFFE3, John RIPMEESTER3, Jean-Baptiste TARY1, Jean-Luc CHARLOU1, Pierre Henry5, Louis GÉli1
1. IFREMER, Centre de Brest, Unité des Géosciences Marines, FRANCE ; 2. Institut Polytechnique LaSalle Beauvais, Département des Géosciences, FRANCE ; 3. Division of Emerging Technologies, National Research Council Canada, CANADA; 4. US Geological Survey, Menlo Park, CA USA; 5. CEREGE / Collège de France, FRANCE ; 6. IFREMER, Centre de Brest, Unité des Environnements Profonds, FRANCE

    The Western High, in the Sea of Marmara, is characterized by a complex fluid circulation system involving free gas migrating through the sediment and bubbling at the seafloor, pore-fluid and oil seepages as well as gas hydrate occurrence. Geochemical analyses have been carried out on gas-hydrate and pore-fluid samples to provide further evidences regarding both the link between the petroleum system of the Thrace basin and the hydrate deposit, and the role of the North Anatolian Fault (NAF) in the fluid migration.

    Thus, gas hydrates were analyzed by gas chromatography for quantitative determination of gas composition, powder X-ray diffraction for determination of the structural type of the hydrates, solid state 13C NMR for defining the locations of gas molecules in hydrate cages, SEM and TD-GC-MS for identification of dissolved compounds. Methane (~70%) was the main gas component of the hydrate samples which also contain relatively high contents of propane (~19%) and isobutane (~9%) as shown from previous study. The powder X-Ray diffraction patterns of the hydrate samples are indexed as structure II hydrate and the NMR chemical shifts of the gases in the hydrates show that methane is not only mainly found in the small cage of sII hydrate but also partly in the large cage, while ethane, propane and isobutane are found exclusively in the large cage. In addition, results from TD-GC-MS and ionic chromatography analyses of pore fluids collected from cores recovered at few kilometers away reveal the presence of a large variety of dissolved heavy hydrocarbons. These analyses confirm that the gas hydrate deposit represent a hydrocarbon-concentrating sedimentary interval supplied by a leaky petroleum system partly through the NAF.